Square footage is the floor area of a room, measured in square feet. It is the starting point for flooring, tile, carpet, paint, and heating and cooling estimates, so a small measuring error can change how much material you order.
Summary: key takeaways
- For a rectangle, square footage = length × width, both measured in feet.
- Measure inside the walls, at the longest and widest points, and keep all measurements in the same unit.
- Break an L-shaped room into two non-overlapping rectangles, calculate each one, and add the results.
- Do not measure the empty corner of an L-shape as if the room were a full rectangle.
- Add a waste allowance for flooring or tile only after you have the room’s true area.
How to measure a rectangular room
Measure the length of one wall and the width of the adjoining wall, inside the room, in feet. If a measurement is in feet and inches, convert the inches first: 6 inches is 0.5 feet, so 12 feet 6 inches is 12.5 feet. Then multiply. For example, a room 12 feet long and 15 feet wide is 12 × 15 = 180 square feet. The Square Footage Calculator uses the same length × width method, so you can check a rectangular room there before you move on to material quantities.
How to handle an L-shaped room
An L-shaped room is two rectangles joined together. Draw the shape on paper, draw one straight dividing line so the two rectangles do not overlap, label each rectangle’s length and width, and calculate them separately. The dividing line can go either way; the total is the same as long as the rectangles do not overlap and together they cover the whole floor. Measure each part at its own longest and widest points, and watch for a closet or alcove that should be counted as its own small rectangle rather than guessed.
Worked example: an L-shaped room
Take an L-shaped living room split into Rectangle A and Rectangle B:
- Rectangle A: 20 feet × 14 feet = 280 square feet.
- Rectangle B: 10 feet × 8 feet = 80 square feet.
- Total: 280 + 80 = 360 square feet.
That 360 square feet is the room’s floor area. If you were ordering flooring with a 10% waste allowance, as in the Flooring Calculator, you would order 360 × 1.10 = 396 square feet. The allowance is for cuts and waste, not extra floor area, so keep the two numbers separate in your notes.
Room shapes at a glance
| Room shape | How to measure it | Formula |
|---|---|---|
| Rectangle | Length and width inside the walls | Length × width |
| Square | One side, inside the walls | Side × side |
| L-shape | Split into two non-overlapping rectangles | Rectangle A + Rectangle B |
| Triangle | Base and perpendicular height | 1/2 × base × height |
| Circle | Radius from centre to edge | 3.1416 × radius × radius |
From area to material
Once you have the area, the next step depends on the material. Tile is usually planned by area plus a waste allowance and grout joints, which the Tile Calculator can estimate, while carpet is commonly ordered by area with attention to roll width and seams, as in the Carpet Calculator. For all three, re-measure a room that has an irregular corner, a bay, or a built-in, rather than rounding it to the nearest rectangle. A few square feet of error is normal to correct at the ordering stage; a whole missing wing of an L-shape is not.
Common mistakes to avoid
- Mixing feet and inches in the same multiplication without converting first.
- Measuring outside the walls, or including an adjoining hallway, and calling it one room.
- Counting the same floor area twice when splitting an L-shape into overlapping rectangles.
- Subtracting nothing for a large built-in, or subtracting a small closet that is actually usable floor space.
Frequently asked questions
Do I include closets in square footage? Include a closet only if it is part of the room you are flooring or measuring; otherwise measure it separately and note it as its own area.
What if the room is not a clean L-shape? Split it into as many rectangles and triangles as needed, calculate each piece, and add them. Keep a sketch so you can check that no piece overlaps another.
Should I round up? Keep the exact total for the room area, then round up only the material order, after applying a waste allowance. Rounding the room itself hides the error.
Is square footage the same as floor area? In this guide, yes: both mean the area of the floor, in square feet, measured inside the room.
Planning-only disclaimer: This guide is for planning only. It does not replace a site measurement by a qualified professional, and material quantities should be confirmed with the supplier and the product’s installation instructions before ordering.